Conservative MP Russ Hiebert, seen here promoting his private members bill to force unions to disclose their spending details last year, maintains his bill is constitutional despite critics who point out its weaknesses and inconsistencies. (Adrian Wyld/Canadian Press)

Call it the Rathgeber clause: Liberals in the Senate are seeking to amend a Conservative bill forcing disclosure of union expenses saying it ought to match another Conservative bill on disclosure of public sector salaries.

That bill had been sponsored by backbench Tory MP Brent Rathgeber and had sought the publication of which civil servants made more than $188,000 a year.

The committee charged with studying the bill reported that it wonders whether the law is constitutional and said it is also concerned about the cost of implementation and the vagueness as to whom the legislation would apply.

And Tory Sen. Hugh Segal has also spoken out against the proposed legislation, calling it bad public policy and questioning the wisdom of dispatching revenue agents to monitor its implementation.